1. Technical Field
The present invention relates to a dynamic-pressure bearing device having a configuration in which an ionic liquid is charged into a bearing space formed in between a shaft piece and a sleeve. The present invention relates further to a disk drive in which such a dynamic-pressure bearing device is installed, and to a method of keeping such a dynamic-pressure bearing device in storage.
2. Description of the Related Art
The development of dynamic-pressure bearing devices capable of supporting various rotary components stably even under high-rpm operating conditions has been progressing in recent years. In dynamic-pressure bearing devices the sleeve part and the shaft piece, which is inserted into the sleeve part with the one being rotatable relative to the other, are each furnished with dynamic-pressure surfaces, and the bearing devices are configured with the sleeve-section dynamic-pressure surfaces arranged opposing the shaft-component dynamic-pressure bearing surfaces. The clearances in between the dynamic-pressure surface pairs disposed in opposition are filled with dynamic-pressure fluid consisting of a liquid such as oil, or a gas such as air. The pairs of dynamic-pressure surfaces and the dynamic-pressure fluid that fills the intervals between them constitute dynamic-pressure bearing sections. Thus, dynamic-pressure devices are configured so that in the dynamic-pressure bearing sections dynamic pressure is produced in the dynamic-pressure fluid when the sleeve part spins or the shaft piece spins, as either of which will be the case depending on the design; it is this dynamic pressure that operates as shaft-supporting force in the dynamic-pressure devices.
A variety of dynamic-pressure fluids are employed in such dynamic-pressure bearing devices. In selecting the dynamic pressure fluid for the devices, balancing viscosity with extent of vaporization is primarily taken into consideration. Ordinarily an ester-based oil is adopted. To guarantee the longevity of the bearing devices, the pace at which a lubricating liquid evaporates has to be kept down. In small-scale dynamic pressure bearing devices in particular, because the surface area of the lubricating liquid tends to be relatively large with respect to the volume of lubricating liquid that the bearings can store, reducing the pace of evaporation is crucial. Lubricating liquids whose pace of evaporation is low, however, generally have a high viscosity. In dynamic-pressure bearing implementations in which a high-viscosity lubricating liquid is used, losses in the bearing devices are significant, making it difficult to achieve satisfactory performance.
Meanwhile, there are also applications that call for electrical continuity between the bearing-device shaft-component section and sleeve section, as is the case with disk drives for example. Such cases require that the dynamic-pressure fluid be lent electroconductivity. One method of lending electroconductivity to a dynamic-pressure fluid is to add a conductivity-imparting agent to the fluid. Nevertheless, the addition of a conductivity-imparting agent can give rise to problems such as deteriorating the wearability (resistance to wear) of the fluid, or else causing evaporation of the fluid to accelerate.